Lint indicator system



United States Patent 3,484,772 LINT INDICATOR SYSTEM Anthony Niewyk, St. Joseph, and James L. McConnell,

Stevensville, Mich, assignors to Whirlpool Corporation, Benton Harbor, Mich., a corporation of Delaware Filed July 6, 1966, Ser. No. 563,167 Int. Cl. G08!) 21/00; G01n 21/12; Btlld 51/00 U.S. Cl. 340236 9 Claims ABSTRACT OF THE DISCLOSURE Apparatus for the detection of lint in a fabric treatment appliance is disclosed. The appliance may be, for example, a clothes dryer and includes a light permeable filter for entrapping lint released by the fabrics. The apparatus includes a light source positioned to pass light through the filter and a light sensitive element positioned to receive the light passed through the filter. An oscillator is controlled by the light sensitive element in such a manner as to be biased to prevent oscillations when the filter is unclogged and allowed to oscillate when the filter is clogged. The oscillator controls a light which is made to flash when the oscillator oscillates and is turned off when the oscillator is prevented from oscillating. Thus, the operator of the appliance is alerted by the flashing light of an undesirable build up of lint.

This invention relates to apparatus for the detection of line in a fabric treating appliance, such as a clothes dryer, and more particularly to apparatus for alerting the operator of the appliance to the presence of an undesirable level of lint built up in the lint trap associated with the appliance.

Conventional clothes dryers available today include a clothes receiving drum provided with an air inlet and an air outlet. A fan positioned cooperatively with the exhaust opening exhausts the air from the drum and discharges it through a discharge passageway. In order to trap the lint carried by the air, a lint trap may be pro vided and positioned at the discharge side of the fan. This trap may consist of a screen or the like permitting passage of air therethrough while filtering out the lint carried thereby. Asthe drying process continues, lint bui1d-up on the screen takes place.

Since an accumulation of lint on the screen would materially reduce or cut-off air flow through the dryer and result in overheating or scorching of the fabrics contained therein, it is desirable that the operator be alterted to such a build-up of lint. Previously, the operator was called upon the inspect to screen periodically and decide for himself when this undesirable condiiton existed. To avoid operator misjudgement or negligence, it is proposed by this invention to automatically bring this undesirable condition to the attention of the operator.

Essentially the features of the invention are accomplished in the following general manner:

A source of light is positioned to pass light through the lint screen and a light sensitive element is positioned to detect light passing through the screen. The light sensitive device is part of an electronic circuit. This circuit is one which has two modes of operation. The mode of the circuit is determined by an electrical characteristic of the light sensitive device. For instance, this characteristic may be resistance. As an illustration, if the resistance of the light sensitive device as determined by the amount of light detected thereby, is below a certain predetermined value, then the electronic circuit operates in its first mode. If the resistance of the light sensitive element 13 is above this predetermined value, the electronic circuit operates in its second mode. The resistance of the light sensitive device may be a function, either direct or inverse, of the amount of light passing through the lint screen. The amount of light is in turn determined by the amount of lint build'up on the screen. For convenience, the first mode may be identified as the undesirable lint level mode and the second as the tolerable lint level mode.

It is, therefore, an object of the present invention to provide in a laundry appliance such as a clothes dryer having a lint screen, control means for providing the operator with an automatic indication of the mode of operation of the dryer, that is, a tolerable lint level mode or an undesirable lint level mode.

It is a further object of the present invention, as will be more fully explained subsequently, to minimize the effects of the supply line voltage fluctuation on the indicating circuitry.

It is a still further object of the invention to provide indicating circuitry in which some of the active elements of the circuitry function as the indicators.

In the drawings:

FIGURE 1 is a schematic illustration partly in section, showing one form of the present invention;

FIGURE 2 is an illustration of one form of electrical circuitry that may be employed in accordance with the present invention, and

FIGURE 3 is a graph plotting voltage against current illustrative of a typical neon bulb that may be employed in the circuitry of the present invention.

Referring to FIGURE 1, there is shown the environment of a dryer including the dryer housing 30, drum 31, fan 32, lint filter 33, and exhaust passageway 34. These environmental elements are illustrative only and are not, per se, part of the present invention. The lint filter 33 is shown as a screen positioned at the exhaust side of the fan 32 and mounted by any conventional means such as brackets 10.

The fan exhausts the air from the drum 31 and discharges it through the lint screen 33 to the exhaust passageway 34. The lint screen 33 filters the air and produces line build-up thereon.

A source of light 11 is mounted on one side of the lint filter 33 and connected electrically to an AC. power source 12. On the other side of the filter 33 is mounted a light sensitive element 13. This element 13 is electrically connected to an electronic circuit including a free-running astable multivibrator, shown diagrammatically at 14. The multivibrator 14 is electrically connected to a DC. power source 15 which, in turn, is connected to the AC. power source 12.

Referring now to FIGURE 2, the AC. power source 12 is connected across lines L and L Connected in L is the rectifying diode 16. The rectified output of diode 16 is developed across resistor 17 and capacitor 18 to provide an unregulated DC. voltage. This DC. voltage is fed to the astable multivibrator 14. The multivibrator 14 includes resistors 20 and 21, capacitor 22, neon bulbs 23 and 24, and the light sensitive element 13 which is shown here as a light sensitive resistor. The neon bulb 24 is positioned on the exterior of the clothes dryer in a position where it can be readily observed by the operator (see FIGURE 1). Neon bulb 23 on the other hand is not visible to the operator. A source of light in the form of a lamp 11 is electrically connected across the AC. power supply 12 and is connected in series with a current limiting resistor 25. The lint filter or screen 33 is positioned intermediate the light source 11 and the light sensitive resistor 13.

Assuming that the lint filter is free of lint so that a maximum amount of light reaches the light sensitive resistor 13, and assuming further that the characteristics of resistor 13 are such that its resistance is inversely proportional to the amount of light impinging on it, then the resistance of 13 would be at a minimum. This being the case, most of the voltage developed by the DC. power source will appear across resistor 21 in the leg including resistor 21 and resistor 13. Therefore, the voltage across resistor 13 and hence across bulb 24 will be insufficient to cause bulb 24 to fire. Under these conditions bulb 24 is in a non-conductive state.

Current from the DC. power source flows through resistor to charge capacitor 22. At some point along the charging path of capacitor 22, the voltage across neon 23 will reach the firing potential. The bulb 23 will fire and will conduct current therethrough. The voltage will then drop from the firing potential to the maintaining potential. It can thus be seen that under the conditions assumed, that is, no lint on the lint filter, bulb 23 willbe on and bulb 24 will be off. This is the tolerable lint level mode of operation of the electronic circuit. This mode will continue until the lint level build-up reduces the light detected by resistance 13 whereby its resistance determines a change in the mode of the circuit.

Now assume that the lint build-up on the screen 33 has reached an undesirable level. This means that the light impinging on light sensitive resistor 13 has decreased so that its resistance has substantially increased. This being the case, and resistor 13 and resistor 21 functioning together as a voltage divider, there now will be sufficient voltage across resistor 13 to fire bulb 24. As seen in FIGURE 3, in which is plotted the V/I characteristics of a typical neon bulb are shown, once the neon bulb 24 has fired the voltage across it drops from a firing voltage V to a lower maintaining voltage V This sudden decrease in voltage is coupled to the anode of neon bulb 23 by means of the capacitor 22 and causes the voltage across the neon bulb 23, which up until this time has been conducting, to fall below its maintaining voltage, and, thus, pass into a non-conductive state.

The capacitor 22 now begins to charge through resistor 20, and in the voltage across neon bulb 23 increases until it reaches its firing voltage. Once the neon bulb 23 has fired, the voltage across it drops from its firing voltage V, to its lower maintaining voltage V This sudden decrease in voltage is coupled to the anode of neon bulb 24 and causes the voltage across bulb 24 to fall below its maintaining voltage and pass into a non-conductive state. The capacitor 22 now begins to charge in the reverse direction and the voltage across neon bulb 23 will increase until its firing voltage is reached and it fires. The cycle then continues to repeat so long as the resistance of light sensing element 13 continues to remain above a preselected value as a result of sensing a reduced amount of light due to an undesirable level of lint build-up.

It can be seen that when the build-up of lint on the lint screen has reached a predetermined level, the circuit switches modes of operation. In the tolerable lint level mode, the neon bulb 24, which is visible to the operator, is in its off or nonconductive condition to thereby indicate that the lint level is acceptable. In the undesirable lint level mode neon bulb 24 will be intermittently fired to thereby flash on and off and indicate to the operator that the lint level is not aceptable. It will be readily apparent that although the indication of an undesirable lint level is shown herein as a flashing light, other indication means, either audio or visual could be provided.

It will be noted that no means has been provided to regulate the DC. power supply output. The proper selection of the tolerances of the various components in the electronic circuit coupled with the fact that the system is to a certain extent self-compensating for line voltage fluctuations obviates the need for regulating the output of the DC. power supply. The self-compensating feature of the system will be best understood by considering the condition where the line voltage increases above a normal level, whereupon the intensity of light given off by the light source 11 will increase. This would normally mean that more lint would collect on the screen before the resistor 13 would cause the flashing light indication to operate. However, increasing the line voltage will likewise increase the D.C. voltage source output, meaning a greater voltage across the voltage divider 21-13. The net effect is that the value of resistor 13 will have to increase less in order for the voltage across neon 24 to reach the firing voltage. These two items, that is, increased intensity of the lamp 11 and a decrease in the value of resistor 13 necessary to fire neon 24, compensate for each other to a certain extent and the amout of lint build-up necessary to cause the flashing indication will tend to remain substantially constant even though the line voltage may fluctuate.

What is claimed is:

1. In a fabric treatment apparatus having a chamber for receiving fabrics to be treated, alight permeable filter for entrapping lint released by said fabrics, means for transporting lint from said chamber to said filter, a light source positioned to pass light through said filter wherein the amount of light permeating said filter is a function of the lint build-up thereon, and control means for providing an indication of lint build-up on said filter, said control means comprising: a light sensitive element positioned to detect light passing through said filter from said light source, said light sensitive element having an electrical characterstic that varies in proportion to the amount of light detected thereby through a range of values on opposite sides of a preselected value; an oscillator circuit connected to said light sensitive element and controlled thereby, said oscillator circuit operating in an oscillatory mode indicative of an undesirable level of lint built-up on the filter when the electrical characteristic of said light sensitive element is within a range of values on one side of said preselected value, and operating in a nonoscillatory mode indicative of a tolerable level of lint build-up on said filter when the electrical characteristic of said light sensitive element is within a range of values on the opposite side of said preselected value; and visual indicator means connected to said oscillator circuit, said visual indicator means producing a flashing output when said oscillator circuit operates in said oscillatory mode and a steadystate output when said oscillator circuit operates in said nonoscillatory mode.

2. The apparatus of claim 1 wherein the electrical characteristic of said light sensitive element is inversely proportional to the amount of light detected thereby.

3. The apparatus of claim 1 wherein said oscillator circuit operates in said oscillatory mode when the electrical characteristic of said light sensitive element is within a range of values above said predetermined value, and wherein said oscillator circuit operates in said nonoscillatory mode when the electrical characteristic of said light sensitive element is within a range of values below said predetermined value.

4. The apparatus of claim 1 wherein the electrical characteristic of said light sensitive element is electrical resistance which is inversely proportional to the amount of light detected thereby, wherein said oscillator circuit operates in said oscillatory mode when said electrical resistance is within a range of values above a predetermined level, and wherein said oscillator circuit operates in said nonoscillatory mode when said electrical resistance is within a range of values below said predetermined level.

5. The apparatus of claim 1 wherein said visual indicator means is a neon bulb for providing an indication of the mode of operation of said oscillator circuit.

6. The apparatus of claim 1 wherein said oscillator circuit is a free running astable multivibrator.

7. The apparatus of claim 6 wherein said visual indicator means is a neon bulb, said astable multivibrator operable to intermittently fire said neon bulb during said oscillatory mode, and to render said neon bulb non-conductive during the nonoscillatory mode.

8. The apparatus of claim 6 wherein said astable multivibrator includes first and second legs connected across a DC. power supply, said first leg including a series connected first resistor and a first neon bulb, said second leg including a series connected second resistor and a second neon bulb, a capacitor connected between the junction of said first resistor and said first neon bulb and the junction of said second resistor and said second bulb, said light sensitive resistor being connected to said second resister and across said second neon bulb whereby said second neon bulb is continuously non-conductive when said multivibrator is in said nonoscillatory mode and said second neon bulb is intermittently conductive when said multivibrator is in said oscillatory mode, and wherein said visual indicator means includes said second neon bulb.

9. The apparatus of claim 6 wherein said light sensi- UNITED STATES PATENTS 2,554,800 5/1951 Steiner 3l7--l24 XR 3,286,508 11/1966 Spiegel. 3,324,633 6/1967 Revell 55-274 JOHN W. CALDWELL, Primary Examiner D. MYER, Assistant Examiner US. Cl. X.R. 

